Category Archives: Electronics

Electronics

Motorola 2N5160 PNP RF Transistors: new-old-stock, medium old stock, fake stock?

Some of the 1980s, 1990s pulse and signal generators use push-pull power amp stages to provide output levels of +-10 V into 50 Ohms, and similar. These are often discrete circuits, utilizing PNP-NPN small power transistors. While the NPN types are still widely available, there used to be some shortages of 2N5160 PNP transistors. Recently, there are are many offers for “Motorola” branded parts, with datecodes from about 1998 (K98xx) to about 2004 (K04xx). In contrast to the earlier Motorola parts (Rxxxx date codes), these have shiny cases. It is quite unlikely that Motorola actually manufactured RF metal can transistors in 2004… (1999 onwards, Motorola no longer made transistors, but transferred the business to ON Semiconductors).

Strangely, the cans have “KOREAN” stamped into them, in various styles and sizes. Would a fake producer have stock of many different kinds of fake cans? Or did ON Semi produce these parts with some existing stock from the 1990s? Many semiconductor producers actually have decade old wafers in stock that they package whenever there is a need.

Let’s have a closer study. Unfortunately, no electron microscope here. But we do our best. Here the die of the defective HP branded original Motorola part. Red arrow shows the burn mark, defect area.

I sacrificed one of the 0.7 USD suspicious parts with K0439 datecode. To my great surprise, they are exactly identical in die, bonding method, and die attachment method.

A quick function test – put the new K0439 date code 2N5190 into an 5 MHz power amplifier. And working just great at >20 dB gain and about 1 Watt output.

Further, we study the collector-base capacitance, at -28 Volts bias U_CB (note that some datasheets specify “28 Volts U_CB” but this won’t work with a PNP transistor – it is conducting like a diode in C-B, if the collector is positive vs. base).

A test with the trusty HP 4192A, and 2.5 pF measures. Exactly the typical value. Also checked one of the certainly genuine Rxxxx date code transistors, and this measured at about 2.7 pF.

Test done at 1 MHz, and calibrated the 4192A with open and short.

So far, so good. All I can say is that these transistors are good 2N5160, whoever made them.

A low frequency xtal oscillator: Austrian generosity, gold, and crystals

A while ago, an Austrian fellow contacted me for some collectibles, long-range telephone line filters (from carrier multiplex phone lines). Many decades ago, phone lines were used at some 50-100 kHz frequencies, to transmit several (!) calls per wire pair. This required good filter, quartz filters were commonly used.

These are 4-electrode filters that are held only by 4 wires soldered to it. Probably oscillating in some flexing mode.

The electrodes are normally connected diagonally, and with a few resistors and an amplifier, I got the part to oscillate nicely. Be aware that you can’t feed a lot of power to these crystals, so it needs a rather high impedance oscillator circuit.

Resonance is at about 50 kHz.

Also connected the specimen to a HP 3562A analyzer, in swept frequency mode, and good nice response plots. There is another dip at 100 kHz!

The schematic, pretty simple, using a 74HCU04 unbuffered inverter, it is a very handy circuit, and years ago I got several tubes of these… you may use any other type of amplifier, gate, or even transistor circuit to get any such xtal oscillating.

Also did some some study on the temperature effect – heated to 100 degC, the frequency dropped by 200 Hz!

A precision current source: a mirror, and a TL431

There are many uses for a good current source, in particular, to drive a noise generator, Noise Source TWS-N15. Not much to write home about, but because of frequent requests, I am publishing the circuit here. It will work for small current from 2 or 3 mA up to 10 or 20 mA with no problem, and very little drift over temperature and time. For R, uses a good resistor. Input voltage can be up to 35 V, or even higher.

The big crash: Server failure

This blog is hosted by a professional provider, but the manuals archive (which needs quite a bit of storage), and other webpages, and my fileserver, is running on two machines, a Dell OptiPlex FX160 as the main, eco-efficient system (in Germany), and a Dell PowerEdge SC1425 with a Raid 1, 3 TB hard drive system as the backup, and currently my main system in Japan (where I am living on a temporary business assignment). Recently, the SC1425 failed, it just would not start up anymore. Power supply seems OK – likely, a severe issue. Checked all the memory and everything, but to no avail.

After fiddling around for about 2 hours, and still no success, I decided to order a new server – a new old server, Dell PowerEdge 850. Just about 35 Dollars used. Rather than 2x XEON processors, it has a Pentium D, 3.2 GHz Dual-Core. Plenty of power for a web- and fileserver.

A couple of days later, the unit arrived – removed the SATA Raid controller (running on Ubuntu with software Raid), and some BIOS settings (activate SATA, disable Keyboard error, enable boot from USB, default power up status is ON) plus BIOS Update. Also, reconfigured the router to make sure this machine will get all the HTTP requests.

A few tests – the harddrive is working fine, about 100 MB/s (sure there is a cache). The Raid 1 is up with no repairs or anything.

A quick check – also the web server is reachable.

I wouldn’t recommend a single PowerEdge for your super critical applications, but they are pretty good for the current cost, as long as you don’t mind the fan noise.

u-blox GPSDO: a simple, low cost, yet – high performance approach

There are many circuits around in the web, related to GPSDOs, and a more sophisticated design with a self-steering u-blox receiver has been published earlier here. Now I felt tempted to try an easier approach, without the hassle of precision references, operational amplifiers, DAC, and other devices that are great but high cost when you need to avoid noise and other complications.
Essentially, this design is a clean-up PLL, with some monitoring of the receiver, and the PLL health. All monitored by a simple 8 bit microcontroller, an ATMega8-16PU in this case.

We have some elements here, (1) the OCXO and amplifier, distribution amplifier – to provide the outputs, 4 in this case, and a good TTL level 10 MHz signal for the PLL, (2) a u-blox receiver, configured to provide either 5 Hz flashing in non-locked condition (no GPS reception, or no good reception), and 125 kHz, 50% duty cycle as a phase reference in locked condition, (3) the MCU, ATMega8, that is configuring the GPS received, providing a 125 kHz signal derived from the 10 MHz OCXO (the OCXO is used as the microprocessor clock – don’t introduce a new clock in such circuits, which will only lead to spurious signals!), (4) a 74HC86 that is used as a phase detector, and to convert the GPS output (a 3.3 V signal) to 5 V level.

That’s the OCXO and distribution amplifier…

The phase detector…

The controller and PLL filter – a simple two pole filter. It replaces all the expensive references, DACs and opamps of the more sophisticated designs. There is another small, faster filter to convert the phase angle to a voltage – converted by the 10 bit ADC of the ATMega8, 1 bit is about 4 ns.

The circuit full view…

Some first tests turned out well. Monitoring the OCXO phase with a scope…

To do a more thorough tests, without all my various test gear that it back in good old Germany, I used the 10 MHz to run another GPS receiver (after upconverting to a 26 MHz clock), then the NAV-CLOCK message can be used to report phase and drift. The short term stability of the OCXO is better than the GPS, as can be seen, but there is no long term drift – because the OCXO is now steered by the 1st GPS receiver via the PLL (XOR phase detector and loop filter).

The phase detection is done at 125 kHz, a convenient frequency for precise measurement, and high enough for filtering.

About 20 ns of jitter are clearly visible in the u-blox output, because it is running on a 48 MHz internal clock.

The circuit is running well, because of the few parts the cost is low and should be easy to reproduce. Let me know in case you need the ATMega code (written in GCC).

The display shows the phase angle, essentially, the duty cycle of the phase comparator output, the stability of the OCXO voltage (by a low pass algorithm), and the lock condition of the GPS (detected by measuring the frequency with timer0 of the ATMega8, and the INT0 interrupt at rising flank to reset the timer).

Phase noise is very small, there are no visible spurs (the lines seen on the screen relate to recalibration events of the analyzer rather than spurious signals, except those at +-125 kHz – at -90 dBc – probably you can get rid of these by better shielding and compartmentalization).

Sure there could be more sophisticated phase noise measurement, by analyzing the control voltage with a low frequency analyzer. I may proceed with such analysis these days but don’t expect to find much, anyway, would be best to fit the circuit to a shielded box first.

All in all, I believe this is a very workable solution that will give you great performance at lowest cost, and with little effort. Sure it will work with various types of OCXOs, the Trimble unit used is generally very good in terms of drift and phase noise. Be aware that some newer Trimble units aren’t all that good. The OCXO draws about 2 Amps at 12 Volts upon startup, but it is OK to start it with a current limited supply, at about 1 Amp, if you don’t want to overdesign the power supply.

GPSDO: a new 10 MHz distribution (and isolation!) amplifier

Many attempts have been made in the past to provide a low phase noise 10 MHz signal as a frequency reference, however recently I experienced some trouble because of ground loops. Normally no problem to decouple from DC voltages, but still the ground stays connected. The only way to avoid such ground loops is to use potential-free isolation, best using transformers. Capacitive coupling may be an option, but it is best avoided, at least it is though to get good isolation, say 2 kV or above, with capacitors that can transmit 10 MHz, at reasonable cost and size.

I am looking for about 1 V p-p, reasonably square shape output, into 50 Ohms, or TTL level (about 5 V) into high impedance. About 5-10 dBm at the 1st harmonic, 10 MHz. So we need to drive about 15 mA through a 50 Ohm load.

As amplifier elements, I am using 74HCU04 unbuffered inverters, these are balanced for propagation delay, and I have plenty of these in a box. The HCU04 is essentially a single stage inverter, a gate with a pretty good linear region – an amplifier. Propagation delay is about 5 ns at room temperature, so it is good solution to amplify clocks, and so on. We are using it to amplify a 10 MHz signal from an OCXO.

For isolation, looking for some small transformers (generally speaking ethernet transformers will work well), I found the PE-65612NL at low cost (list price is about 4 USD per piece, but some sellers have them at a small fraction of this cost, most likely, from surplus). These are 1:1, 2 kV min, signal transformers originally intended for digital audio signal separation. Good enough for our purposes.

A really affordable offer… sure you can substitute any other reasonable signal transformer that can cope with at least 20 mW, and is reasonably inexpensive.

The schematic – first, a single HCU04 is used to square up the OCXO output, and then distribute to 3 outputs, two are used to drive 2 isolated outputs each (4 outputs total), the other output is routed to a PLL circuit (because this isolation amp is part of a GPSDO). Any phase drift of the 1st stage HCU04 introduced by thermal and other slow effects will be canceled to some part by the GPS loop (because the sampling of the phase is very close to the isolated outputs, only followed by a set of paralleled-up gates) – although I don’t expect such drift.

The resistors were selected as 3×330 Ohm, giving about 100 Ohms source resistance and about 1.4 V pp when terminated in 50 Ohms.

Output power is fairly consistent, like, +-0.2 dBm when comparing 4 units. Fundamental output at 8 dBm is exactly the right range. Probably you can adjust it in the range of 5 to 10 nominal without changing much the other characteristics of the circuit, by changing the resistor values from the paralleled-up gates to the isolation transformer.

u-blox GPSDO: Joe’s and Gisela’s magic generator

In reply to an earlier post, GPSDO Update, I received the following great implementation of a GPSDO using u-blox receivers. The pictures are rather self explanatory.
>>>>
Hello again Simon!
I trust you are well and are enjoying the year end break.

We ( My good Wife and I..) have put your GPSDO software to good use. We used your message processing code almost as is, and added the various functions to drive my specific hardware and DAC, etc.

I have built up the complete GPSDO, with the 1-50MHz Analogue Devices AD9854 Quadrature DDS as a signal generator, provided with a 200MHz clock from the SI5351 PLL.
I also have a ‘signal generator’ output from another Si5351 channel, 1 to 200MHz, and a third channel output. square wave, from the GPS time pulse output, and can set outputs from 1Hz to 10MHz in decade steps.
I used a 7inch NEXTION graphics display for the display and control inputs ( touch screen) – that works very nicely!

I have run the unit for a few days now, and logged a 48hour period of data, every 10seconds, regarding the clock bias, drift, DAC output voltage etc, and the result looks very good indeed.
I am very pleased with the instrument and grateful for your assistance in providing your code. Thank You!

I have attached a few photos for interest.

Kind regards, and have a very good Christmas!

Joe and Gisela.
>>>>

TWS-N15 Noise Source 10 MHz-2 GHz: a few more sets

Coming back to an earlier post, Noise source design, I wanted to post the final results, and the looks of these noise sources.

The case is an aluminum extrusion design, and the lids are milled to accomodate the BNC and SMA connectors. The SMA is a really high quality connector. No point in using a noise source with a cheap connector – you are normally going to connect and disconnect this often.

The constant current supply is optimized for the maximum noise output, normally, about 8 mA. The design is a current mirror, with a TL431 precision reference.

The noise section is soldered with 0603 SMD mostly, on a FR4 board.

Foam and copper tape to avoid any foreign signals getting into it. Spurious signals can mean big trouble with noise measurements.

Return loss, I think it is pretty good.

SWR.

After some optimization of the circuit, the ENR output is now pretty flat, even with no specially expensive noise diode.

After all, pretty happy with the device, and others are happy two, as I give them away at low cost. If you need one, let me know.

Crimping Molex Contacts: 3.96 mm KK Style, new capability add to my workshop

For year I have been using various Molex style connectors, 2.5 mm, 3.96 mm, and so on, but never by crimping own contacts. Criming is a special art, and if not done properly, it can cause all kinds of reliability issues. So I usually purchased pre-crimped wires, and just assembled them for contact blocks. In other cases, I just used regular pliers to mount wires to contacts, and soldered them in (best, to pre-tin the wire, then mount it in the contact with small pliers, then solder it in – this will result in a very reliable connection. Also, never use low quality wire, only full copper core, heavily tinned wire, UL 1007 or similar.

But why not try to crimp contacts ourselves and add a new capability to the workshop? So I went ahead, and ordered a low cost pair of crimping pliers, EUR 12, not bad.

It made it from China to Japan very quickly, delivered by a friendly postman (here they are very friendly). That’s the tool: quality looks quite OK, and the steel is pretty hard. Sure this is not a high throughput production tool – I am looking at a few 10s of contacts every year, not 1000s.

Step 1, remove the insulation from the wire, and get the contact and pliers ready.

Step 2, insert the contact in the pliers, and close it until flush (don’t apply much force).

Step 3, insert the wire, and crimp the inner connection. Don’t get any of the insulation caught up by the crimp. It is a bit inconvenient to get the contact out of the pliers, probably will make a special tool for it (a U-shape bent piece of steel sheet metal to push out the contact).

Step 4, Inspect the inner crimp. Use a magnifier if necessary (make sure no plastic and insulation got into the crimp area). Pull on the wire, it must be firmly held (a properly crimped wire can’t be pulled out by any reasonable force).

Step 5, slightly close the insulation crimp using the tip of the pliers.

Step 6, establish the insulation crimp.

Step 7 – It’s ready. Inspect. Carry out pulling test.

HP 8412A Phase Magnitude Display: really unusal supply voltages…

Looking for the CRT front bezel and frame to fix another unit, I found this 8412A Phase Magnitude Display on a Japanese auction site for EUR 8 plus shipping, really affordable! Also, I believe it to be a great source of spare parts, because there are many of the HP standard semiconductors of the 70s inside.

The unit arrived in great shape, almost too good to take it apart – maybe we can use it for something cool, like a CRT clock or some soundwave visualization unit?

How to get it to work – checked the 8412A manual, and, unfortunately, it needs a whole lot of unusual supply voltages (the 8412A slides into the 8410A/B Network Analyzer mainframe) – not easy to operate it without the mainframe. 175 Volts AC, to drive the CRT and 6.3 VAC heater, and +-20 VDC, for the other circuits.

Some pictures of the unit…

The dangers of high voltage are fairly obvious!!

Quite similar to other HP units – amazing how often they recycled the design!

2.000 kOhm, +- 0.05% resistors, a matched pair – not bad! Definitely, a lot of good parts in this unit, including high voltage parts, a good CRT, many semiconductors and transistor pairs, mica capacitors, etc.

HP even supplied a small test board to make service and adjustment easier! Great!!